I would expect that commercial Al alloys like 2024, 6061 and 7075, which have been heat-treated (age-hardened), have lower ductility than pure Al, and thus the fatigue behavior/fracture toughness for pure Al is better than for the alloys. Is this correct?
Thanks
If you want, send an email to Giampaolo Campana. He is an especialist in aluminum.
No, it is not correct, at least for fatigue.
See Chapter 5, 5.1.1 in "Properties of Aluminum Alloys: Fatigue Data and the Effects of Temperature, Product Form, and Processing" by John Gilbert Kaufman. (Available as a Google e-book)
No. The mechanical properties depend on the heat treatment state of Al and its alloys as well as on loading conditions such as temperature and loading rate. But in most cases, it is not correct that pure Al shows better fatigue behaviour and fracture toughness than common aluminum alloys.
No.. I agree with Michel The temperature condition, composition also plays a role apart from ductility
It is harder to initiate a fatigue crack in a stronger material than a weaker material. Crack initiation is driven by slip at the surface or a defect. If the dislocations find it harder to move then it will be more difficult for persistent slip bands to form and eventually form a crack. A good example of this is the strong aluminium alloy 2024 when clad in pure aluminium for enhanced corrosion resistance. This is the stuff aircraft fuselage is made from btw. The initiation fatigue performance of the clad alloy is a lot worse than the unclad alloy.
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